Torque sensor for vehicle steering system

ABSTRACT

A torque sensor for a vehicle steering system having a power source, an oscillator and an offset voltage circuit part includes a current amplifier, first and second coils that are in series and connected at both ends thereof to output terminals of said current amplifier and said offset voltage circuit part, respectively, and first and second resistances that are in series and connected in parallel to said first and second coils. The torque sensor further includes first and second waveform selecting parts, first and second peak detectors, a first differential amplifier, and a first voltage-current converter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is based on, and claims priority from, KoreanApplication Serial Number 10-2004-0104194, filed on Dec. 10, 2004, thedisclosure of which is hereby incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The present invention relates to a torque sensor for a vehicle steeringsystem adapted to prevent a distortion phenomenon of a torque detectingsignal due to a temperature variation of a coil part of the torquesensor or the like.

BACKGROUND OF THE INVENTION

Generally, an Electronic Control Unit (ECU) of an Electrical PowerSteering (EPS) system controls the steering of a vehicle by detectingsteering torque according to the manipulation of a steering wheel of adriver through a torque sensor.

In the torque sensor of the EPS system, an output waveform of the torquedetecting coil is sampled through a sampling pulse circuit.

The phase and amplitude of the output signal vary according to animpedance variation of the torque detecting coil. When a phase variationoccurs due to environmental effect such as a temperature variation, orthe like if a precise sampling of the signal is not executed,reliability of the torque sensor deteriorates by, for example, adistortion phenomenon of the torque detecting signal.

SUMMARY OF THE INVENTION

Embodiments of the present invention are provided to prevent adistortion phenomenon of a torque detecting signal caused by a variationof the amplitude and phase of an output signal of a coil part(temperature correcting coil and torque detecting coil) due to atemperature variation of the coil part of a torque sensor for a steeringsystem or the like.

A torque sensor for a vehicle steering system includes a power sourcefor supplying power. An oscillator oscillates by receiving a voltagefrom the power source. An offset voltage circuit part generates anoffset voltage by using the voltage applied from the power source. Acurrent amplifier outputs an offset voltage and an alternating currentvoltage, which is in-phase with a voltage outputted from the oscillator.A first and second coil are in series and connected at both ends thereofto output terminals of the current amplifier and the offset voltagecircuit part. A first and second resistance are in series and connectedin parallel to the first and second coil. A first and second waveformselecting part receive an alternating current voltage from a contactpart of the first and second coil and from a contact part of the firstand second resistance and then select and output a half-period of thealternating current voltage. A first and second peak detector detect apeak value of each output voltage of the first and second waveformselecting part. A first differential amplifier executes differentialamplification by receiving voltages from the first and second peakdetector. A first voltage-current converter outputs a torque signal byconverting a voltage, which is outputted from the first differentialamplifier, into a current.

The torque sensor further includes a third and fourth resistance thatare in series and connected in parallel to the first and second coil. Athird and fourth waveform selecting part receive an alternating currentvoltage from a contact part of the first and second coil and a contactpart of the third and fourth resistance and then select and output ahalf-period of the alternating current voltage. A third and fourth peakdetector detect a peak value of each output voltage of the third andfourth waveform selecting part. A second differential amplifier executesdifferential amplification by receiving voltages from the third andfourth peak detector. A second voltage-current converter outputs afail-safe torque signal by converting a voltage, which is outputted fromthe second differential amplifier, into a current.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the nature and objects of the presentinvention, reference should be made to the following detaileddescription with the accompanying drawings, in which:

FIG. 1 is a block diagram of a torque sensor for a steering systemaccording to an embodiment of the present invention;

FIG. 2 illustrates a waveform of an output voltage of an oscillatoraccording to an embodiment of the present invention;

FIG. 3 a illustrates a waveform of an output voltage of a currentamplifier according to an embodiment of the present invention;

FIG. 3 b illustrates a waveform of an output voltage of an offsetvoltage circuit part according to an embodiment of the presentinvention;

FIG. 4 illustrates a waveform of an output voltage of a first and secondcoil contact part according to an embodiment of the present invention;

FIG. 5 illustrates a waveform of an output voltage from a first andsecond waveform selecting part and a third and fourth waveform selectingpart according to an embodiment of the present invention; and

FIG. 6 illustrates a waveform of an output voltage from a first andsecond peak detector and a third and fourth peak detector according toan embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, an embodiment of the present invention is providedto prevent a distortion phenomenon of a torque detecting signal causedby a variation of a phase and amplitude of a signal outputted from acoil part (temperature correcting coil and torque detecting coil) due toa temperature variation of the coil part of a torque sensor for asteering system or the like. This is achieved by selecting a waveformand detecting a peak value after oscillating an oscillator via anapplied voltage.

The torque sensor according to the embodiment of the present inventionincludes a power source (E) for supplying power. An oscillator 2oscillates by receiving a voltage from power source (E). An offsetvoltage circuit, part 6 generates an offset voltage (V_(offset)) byusing the voltage applied from power source (E). A current amplifier 4outputs an offset voltage (V_(offset)) and an alternating current (AC)voltage, which is in-phase with a voltage outputted from oscillator 2. Afirst and second coil (L1, L2) are in series and are connected at bothends thereof to output terminals of current amplifier 4 and offsetvoltage circuit part 6. A first and second resistance (R1, R2) are inseries and are connected in parallel to first and second coil (L1, L2).A first and second waveform selecting part 8 a, 8 a′ receive analternating current (AC) voltage from a contact part (A) of first andsecond coil (L1, L2) and from a contact part (B) of first and secondresistance (R1, R2) and then select and output a half-period of the ACvoltage. A first and second peak detector 10 a, 10 a′ detect a peakvalue of each output voltage of first and second waveform selecting part8 a, 8 a′. A first differential amplifier 12 a performs differentialamplification by receiving voltages outputted through first and secondpeak detector 10 a,10 a′. A first voltage-current converter 14 a outputsa torque signal (Ts) by converting a voltage, which is outputted fromfirst differential amplifier 12 a, into a current.

The torque sensor according to the embodiment of the present inventionis configured to detect a fail-safe torque.

A third and fourth resistance (R1′, R2′) are in series and connected inparallel to first and second coil (L1, L2). A third and fourth waveformselecting part 8 b, 8 b′ receive an AC voltage from contact part (A) offirst and second coil (L1, L2) and a contact part (B′) of third andfourth resistance (R1′, R2′) and then select and output a half-period ofthe AC voltage. A third and fourth peak detector 10 b, 10 b′ detect apeak value of each output voltage of third and fourth waveform selectingpart 8 b, 8 b′. A second differential amplifier 12 b executesdifferential amplification by receiving voltages outputted through thirdand fourth peak detector 10 b, 10 b′. A second voltage-current converter14 b outputs a torque signal (Ts′) by converting a voltage, which isoutputted from second differential amplifier 12 b, into a current. Thefail-safe torque is required to make a steering by using torquedetecting signal (Ts′) when an abnormality of torque detecting signal(Ts) or the like occurs.

First and second waveform selecting part 8 a, 8 a′ and third and fourthwaveform selecting part 8 b, 8 b′ can preferably be half-wave rectifiercircuits.

The operation of the torque sensor according to the embodiment of thepresent invention will now be described with reference to drawings.

As illustrated in FIG. 1, when the power is provided from power source(E) to oscillator 2, an oscillating voltage of oscillator 2 is appliedto current amplifier 4. An output waveform (Va) of oscillator 2 isillustrated in FIG. 2.

Current amplifier 4 outputs a direct current (DC) voltage (V_(offset))and an AC voltage (Vb), which is in-phase with an output voltage ofoscillator 2, into a temperature correcting coil (L1, first coil) (seeFIG. 3 a). Simultaneously, a DC voltage (V_(offset)) is inputted into atorque detecting coil (L2, second coil) through offset voltage circuitpart 6 generating the offset voltage (V_(offset)) by using the powerfrom power source (E) (see FIG. 3 b).

Temperature correcting coil (L1, first coil) and torque detecting coil(L2, second coil) are connected in series between an output terminal ofcurrent amplifier 4 and an output terminal of offset voltage circuitpart 6. An amplitude of an AC voltage of a contact part (A) betweentemperature correcting coil (L1) and torque detecting coil (L2) variesaccording to the difference between inductance of temperature correctingcoil (L1) and inductance of torque detecting coil (L2) (see FIG. 4).

First and second resistance (R1, R2) are connected in parallel totemperature correcting coil (L1) and torque detecting coil (L2). If thevalues of first and second resistance (R1, R2) are identical to eachother, only the DC voltage (V_(offset)) is applied into contact part(B). In case third and fourth resistance (R3, R4) have an identicalvalue, the voltage of contact part (B′) and the voltage of contact part(B) are identical.

Voltages of contact parts (A, B) of first and second coil (L1, L2) andfirst and second resistance (R1, R2) are applied to first waveformselecting part 8 a and second waveform selecting part 8 a′,respectively. A signal waveform (Vd) outputted through first and secondwaveform selecting part 8 a, 8 a′ is shown in FIG. 5. As shown in FIG.5, a signal outputted through first and second waveform selecting part 8a, 8 a′ (half-wave rectifier circuits) is a signal that has selectedonly a half-period of the applied AC voltage.

In reference to FIG. 6, the output signal from first and second waveformselecting part 8 a and 8 a′ is applied into first and second peakdetecting part 10 a, 10 a′, respectively, to detect a peak value (Vp) ofthe applied AC signal (Vd1-Vd3). For overcoming a discordance with asampling pulse generating circuit which conventionally occurs accordingto a variation of an amplitude and phase of coils (L1, L2) due to atemperature variation or the like, a rectification conversion of an ACsignal from oscillator 2 and a detection of a peak value of therectified signal are pre-executed in the embodiment of the presentinvention.

A differential amplification is produced in the voltage supplied tofirst differential amplifier 12 a from first and second peak detectingpart 10 a, 10 a′ and then the differential amplified signal is outputtedas a torque detecting signal (Ts) through first voltage-currentconverter 14 a. The outputted torque detecting signal is inputted intoan Electronic Control Unit (ECU, not shown), thus a steering force isobtained by operating a motor according to torque detecting signal (Ts).

In the fail-safe torque detecting sensor according to the embodiment ofthe present invention, operations of third and fourth waveform selectingpart 8 b, 8 b′, third and fourth peak detecting part 10 b, 10 b′, seconddifferential amplifier 12 b, and second voltage-current converter 14 bare identical to that of the main circuit of torque detecting sensordescribed above. Therefore, fail-safe torque detecting signal (Ts′) isemployed to detect a torque in a fail-safe torque detecting sensor incase of an abnormality of main torque detecting signal (Ts) or the like.

In order to prevent a distortion phenomenon of the outputted torquedetecting signal even in case a phase and amplitude vary due to atemperature variation of the coil part (temperature correcting coil andtorque detecting coil) of the torque sensor or the like, a rectificationconversion through waveform selecting parts of the rectifier circuit anda peak value of a signal converted into rectification are detected afteroscillating oscillator 2 by using the power supplied from power source(E).

The technical concept is not limited to the embodiment of the presentinvention and should be determined by a logical interpretation withinthe scope of claims of the present invention.

As apparent from the foregoing, there is an advantage in the torquesensor for a vehicle steering system in that a distortion phenomenon ofa torque detecting signal according to the phase variation in the coilpart due to a temperature variation or the like is prevented.

1. A torque sensor for a vehicle steering system, comprising: a powersource that supplies power; an oscillator that oscillates by receiving avoltage from said power source; an offset voltage circuit part thatgenerates an offset voltage by using said voltage supplied from saidpower source; a current amplifier that outputs an alternating currentvoltage which is in-phase with a voltage outputted from said oscillator;first and second coils that are in series and connected at both endsthereof to output terminals of said current amplifier and said offsetvoltage circuit part, respectively; first and second resistances thatare in series and connected in parallel to said first and second coils;first and second waveform selecting parts that receive an alternatingcurrent voltage from a contact part of said first and second resistancesand from a contact part of said first and second coils, respectively,and then select and output a half-period of said alternating currentvoltage; first and second peak detectors that detect a peak value ofeach output voltage of said first and second waveform selecting parts; afirst differential amplifier that executes differential amplification byreceiving voltages outputted through said first and second peakdetectors; a first voltage-current converter that outputs a torquesignal by converting a voltage, which is outputted from said firstdifferential amplifier, into a current; and third and fourth resistancesbeing in series and connected in parallel to said first and secondcoils; third and fourth waveform selecting parts that receive analternating current voltage from a contact part of said third and fourthresistances and from a contact part of said first and second coils,respectively, and then select and output a half-period of saidalternating current voltage; third and fourth peak detectors that detecta peak value of each output voltage of said third and fourth waveformselecting parts; a second differential amplifier that executesdifferential amplification by receiving voltages outputted through saidthird and fourth peak detectors; and a second voltage-current converterthat outputs a fail-safe torque signal by converting a voltage, which isoutputted from said second differential amplifier, into a current. 2.(canceled)
 3. The torque sensor as defined in claim 1, wherein each ofsaid first, second, third and fourth waveform selecting parts include ahalf-wave rectifier circuit.
 4. (canceled)